The Detection Of Benzoic Acid,Sorbic Acid And Recombinant Bovine Somatotropin In Milk

Dairy products have extremely high nutritional value,which can regulate human metabolism.Dairy products can promote the bone growth of infant,prevent osteoporpsis in the elderly.Dairy industry is an important part of modern agriculture.To promote the sustainable development of dairy industry can optimize the agricultural structure,increase agricultural income,improve the residents' dietary structure and inhance the national physique.With the rapid development of diary industry in China,the quality and safty issue of dairy products has become the focus of attention.In this thesis,an ultra performance liquid chromatography method has been developed for the simultaneous determination of sorbic acid and benzoic acid in milk.An Ultra performance liquid chromatography tandem mass spectrometry method has been developed to detect recombinant bovine somatotropin in milk.Besides,a total of 202 commercial milk samples from China,including Liaoning,Inner Mongolia,Heilongjiang,Jilin,Sichuan,Shandong,et al.,were determined for benzoic acid and sorbic acid using Ultra performance liquid chromatography to assess the contamination of benzoic acid and sorbic acid in milk,which are commercially available in China.The main research contents and conclusions are as follow:1.An ultra performance liquid chromatography method has been developed for the simultaneous determination of sorbic acid and benzoic acid in milk.The column temperature,the flow rate and the mobile phase ratio have been optimised.The method validation shows that the limits of quantification and the limits of quantitation of this method were 0.01 ?g/mL and 0.03 ?g/m L respectively,recovery rate was in the range of 95.3%~107.3%,relative standard deviation was in the range of 0.9%~10.5%.These data shows that this method can be used for the determination of benzoic acid and sorbic acid in milk products.2.In this study,a total of 202 milk samples commercially available in different regions of China,including Heilongjiang province,Inner Mongolia,Jilin province,Liaoning province,Henan province,Hebei province,et al.,were determined for benzoic acid and sorbic acid using ultra performance liquid chromatography method to assess the contamination of benzoic acid and sorbic acid.The detection rate of benzoic acid and sorbic acid measured were 9.9% and 0.5% respectively.The detection rate of benzoic acid and sorbic acid in ultra-high temperature sterilized milk was 8.13% and 0% respectively.The detection rate of benzoic acid and sorbic acid in pasteurized milk was 16.66% and 2.38% respectively.In addition,the detection rate of benzoic acid and sorbic acid in different types of milk,domestic and imported milk was analyzed by chi-square analysis.The results showed that there was no significant difference in the detection rate of benzoic acid and sorbic acid between ultra-high temperature sterilized milk and pasteurized milk.There were significant differences in the detection rate of benzoic and sorbic acid between domestic milk and imported milk.Considering the natrual content(about 6 mg/L)of benzoic acid in milk,this study analyzed the excessive rate of benzoic acid and conducted a chi-square analysis.The results show that,there was no significant difference between the excessive rate of benzoic acid in ultra-high temperature sterilized milk and pasteurized milk.The results also show that there was no significant difference between the the excessive rate of benzoic acid in domestic milk and imported milk.3.An ultra performance liquid chromatography tandem mass spectrometry method has been developed to detect recombinant bovine somatotropin in milk.Besides,the sample pro-processing parameters were optimised by respponse surface method.Quadratic regression model was developed and the optimum pro-processing parameters were predicted: enzymolysis time is 155.81 min,DTT reaction time is 46.31 minnute,enzyme-to-substrate ratio is 1:59.56.These parameters was adjusted to parameters as follow: enzymolysis time is 156 min,DTT reaction time is 46 min,enzyme-to-substrate ratio is 1:60.The method validation shows that the limits of quantificaiton and the limits of quantitation were 0.71 ng/nL and 2.4 ng/mL respectively.The recovery rate ware in the range of 92.56%~100.35%,the relative standard deviation was lower than 10%.